Air carriers almost always use canned flight plans that never vary,

Most air carrier flight plans are not canned in the sense that the same
flight plan is prefiled and does not ever change. Air carrier flight
plans are typically filed the same day as the flight and do vary
according to weather or flow restrictions.


and they seldom file /G.

If the aircraft is capable of /G then that is what they would file.
Nowadays with the jets pretty much all you see is /Q and /W.